Polyester filaments having improved frictional characteristics



y 1965 E. A. HASELEY 3,184,369

POLYESTER FILAMENTS HAVING IMPROVED FRICTIONAL CHARACTERISTICS FiledJuly 10, 1963 FIG. Ia

INVENTOR EDWARD ALBERT HASELEY ATTORNEY United States Patent POLYESTERFILAMENTS HAVING IMPROVED FRICTIONAL CHARACTERISTICS Edward AlbertHaseley, Grifton, N.C., assignor to E. I.

du Pont de Nemours and Company, Wilmington, DeL, a corporation ofDelaware Filed July 10, 1963, Ser. No. 293,996

5 Claims. (Cl. 161-179) This invention relates to novel filaments andfibers suitable for use in the textile industry. More specifically, theinvention relates to new melt-spun synthetic organic polymer filamentshaving improved frictional characteristics.

Mob-spun synthetic organic polymer fibers, e.g., the poly(ethyleneterephthalate) fibers disclosed in Whinfield et al. US. Patent No.2,465,319, dated March 22, 1949, have become well-known articles ofcommerce and are preferred for many uses because of their outstandingphysical and chemical properties. However, it is recognized that somefeatures of melt-spun fibers are undesirable for some purposes. Inparticular, the remarkable level of surface smoothness of melt-spunfibers has resulted in an undesirably high level of dynamic frictionbetween these fibers and surfaces rubbing against them, which, amongother things, gives rise to high drafting tensions, high tension inrunning threadlines, poor staple processability, and an excessive degreeof wear on machine surfaces in contact with moving yarns.

Among the various methods which have been tried for roughening thesurface of melt-spun synthetic polymer fibers may be mentioned thetreatment of fibers with a chemical etching agent, e.g., a solvent, theincorporation of dispersed insoluble particles in the polymer beforespinning, and the incorporation of soluble materials in the polymerbefore spinning followed by a leaching treatment after spinning whichremoves the soluble material and leaves holes in the fiber surface.Mechanical treatments for embossing a pattern upon fiber surfaces havealso been tried. However, few previously known methods have been foundto give a significant reduction in friction without also adverselyaffecting some other fiber property, e.g., tensile strength.

It is an object of this invention to provide new and improved filamentsand fibers from melt-spun synthetic organic polymers. Another object isthe provision of melt-spun filaments and fibers with improved frictionalproperties. A further object is the provision of oriented polyesterfilaments and fibers having a rough surface, but with other propertiesequivalent to smooth surfaced filaments and fibers. Other objectiveswill become apparent from the description and examples which follow.

The objects of this invention are achieved by the provision of asubstantially oriented synthetic linear condensation polyester fiber(continuous filament or staple) having a surface characterized by aseries of randomly spaced, discontinuous circumferential ridges ofsubmicroscopic size occurring with a frequency between and 130 ridgesper millimeter along the length of the fiber. The fiber is furthercharacterized by the absence of diameter variations in excess of 5% ofthe base fiber diameter, i.e., there is no significant number of sizablebumps or nodules along the length of the fiber.

An important characteristic of the fiber of this invention is theabsence of internal voids, or bubbles, associated with the surfaceridges. The presence of such internal voids in some bumpy or nodularfilaments of the prior art is thought to be a cause of the decreasedtensile 3,184,369 Patented May 18, 1965 ice strength observed in thosefilaments. Preferably, the fibers are free from voids, either internalor etched holes, or dispersed insoluble particles other thanconventional delustrants.

The term discontinuous, as used above, is intended to indicate that amajority of the ridges do not make a complete, closed circle around thecircumference of the filament. In general, the ridges are found to be ofsuch a length that the arc is a minimum of of the circumference andusually there is at least 180 of are. Some of the ridges appear toextend through 270 of arc, but the sub-microscopic nature of thephenomenon makes it difficult to identify and follow any given ridgecompletely around the circumference of the filament.

The use of the term circumferential is intended to indicate that thelong dimension of a ridge travels along the circumference, or perimeter,of the cross-sectional figure made by a plane passing through thefilament at right angles, or nearly so, to the fiber axis. In general,the angle between the fiber axis and a plane containing a given ridgewill fall between 70 and The use of the word circumferential is notintended to restrict the invention to filaments of round cross-section.

The term sub-microscopic is intended to indicate that the height of theridges above the surface of the fiber is less than the theoretical limitof resolving power of the usual light microscope, which is generallystated to be about 0.25 micron. The ridges on the surface of thefilaments and fibers of this invention have a height no greater thanabout 0.2 micron above the fiber surface, and for the most part have aheight falling within the range 0.07 to 0.12 micron.

The characteristic ridges of the fibers of this invention are bestidentified and examined by means of the electron microscope. Standardreplica techniques and shadowing procedures may be used. Suchexamination usually reveals that the ridges are smoothly rounded,wavelike bulges in the fiber surface which are characterized by thesubstantial absence of sharp corners and edges or abrupt changes ofdirection. Because there is no abrupt dividing line between the ridgeand the adjacent fiber surface, the width of a ridge is diificult tomeasure precisely. It has been estimated, however that a majority of theridges have a width in the range of 3 to l0 the ridge height.

Surprisingly, it has been found that the fibers of this inventionexhibit a substantial reduction in rubbing friction in comparison witholder smooth-surfaced meltspun fibers. For example, a drop of 40% ormore in the coefficient of hydrodynamic friction is commonly observed incomparison with similar yarns which do not possess high frequency,submicroscopic transverse ridges as described above. Furthermore, thereduction in friction is obtained without any significant loss intensile strength.

In the drawings, FIGURES 1a, 1b and 1c are diagrammatic illustrations ofthree stages in the formation of the fibres of this invention. FIG. 1arepresents a side view of a portion of an undrawn filament as it wouldappear when greatly magnified. FIG. 1b is a corresponding view of thefilament after initial treatment to produce a multiplicity ofcircumferential surface cracks. Most of these, e.g., cracks 10, 12 and13, are clearly discontinuous in that they do not encircle the filament,but others may appear to follow completely around the circumference,e.g., crack 11. FIGURE 1c is a corresponding view after part of thefilament has been drawn to much smaller diameter. Crack It) is stillvisible on the incompletely drawn part. However, on the completely drawnpart, small ridges 21, 22

A area-,aeo

and 23 occur at positions corresponding to cracks 11, 12 and 13,respectively.

FIGURE 2 is a drawing prepared from a photograph at 1600 magnificationof a typical filament of this invention. An electron microscopeandstandard replica tech.- nique were used, so that a negative surfacereplica was photographed rather than the filament surface shown in thedrawing.

The fibers of this invention may be prepared by a process whichcomprises melt spinning a synthetic linear condensation polyester toproduce unoriented filaments, aging the filaments in contact withcertain crack promoting agents until a fracturable skin'is produced asdescribed more fully below, predrawing the filaments in contact with thecrack-promoting agent by subjecting them about 1.011.'1 times theiroriginal length, disassociating the filaments from the influence of thecrack-promotlng agent, and final-1y drawing the filaments according towellknown drawing procedures to give substantially oriented fibershaving good tensile properties.

Aging the as-spun fiber in contact with certain crackpro rnoting agentsbefore subjecting it tothe initial stretch-' ing operation is importantin obtaining the productof this invention. Aging, in some manner notcompletely understood, changes the character of the fiber surface sothat in the low draw ratio ipredrawing flstep a multiplicity of fine,transverse cracks is formed in the fiber surface. some fashion thepresence of these cracks leads to the formation of sub-microscopicridges inthe subsequent ally not preferred because offstorage problemsin a yarn 'to sutficient tension at low temperature to stretch them toThe liquid chosen for test should not, in general, be

' a solvent or strong swelling agent for the polymer. Appreciablesolvent action by a liquid necessarily eliminates the formation ofsurface cracks. Certain liquid cracking agents whichare otherwisesuitable but which exert a certain amount of solvent or swelling actionon the polymer may be employed provided that the contact time betweenthe liquid and the polymer is kept short enough for cracking to occurbefore the swelling or plasticizing action proceeds to an appreciableextent. 7

The following criteria maybe used for selection of outstanding crackingagents suitable for use in aqueous solutions on polyester fibers:

' (1) The agent should be unsaturated or contain other sources ofunpaired electrons.

(2) The. agent should be sufiiciently soluble or dispersible inwater foraqueous application.

(3) The agent should be liquidat the cracking temperaturc employed inthe process. I

' (4) The agent should not be strongly self-associating (e.g., asdifunctional alcohols or amines) since this re,- duces possibilities forassociation with polymer, which is postulated to be necessary.

5 The agent should be r fairly high molecular 'weight, i.e., above about200.

Observance of the. above criteria has led to the use of high-boilingesters such as butyl stearate and isopropyl myristate, polyet-hers suchas the poly(ethyleneoxide) glycols of molecular weight 400 and 600,poly(ethyleneoxide.) glycol 400 monolaureate, and random copolymers ofethyleneoxideand propyleneoxide, as well as high molecular weighthydrocarbons such aseicosane.

In the predrawing step, the filaments are preferably stretched until thedrawn length is about 1.01 to 1.1 times the undrawn length. "Lessdrawing does not produce a I sufficient number of ridges in the finalproduct to yield a manufacturing plant. Aging times shorter than 2 daysmay significant reduction in friction. On the other hand, too

great a draw leads to significant numbers of denier nonuniformities,nodules, and large size bumps which change the character of thefilamentsto the extent that they no longer can be considered the equivalent ofsmooth-surfaced spinning finish, will'reduce the minimum aging time to 7about 2 hours.

The use of high molecular weight cracking agents is absolutely essentialif the novel filarnents described herein are to be obtained. Lowmolecular weight cracking agents such as acetone, ethanol, dimethylformarnide, or pyridine cause undesired large diameter variations ornodules or else introduce voids into the filaments in present inventionit is believed that the restriction of the melt-spun fibers. Thepredrawing step may be carried out at room temperature or attemperatures up to about 80 C. Above this temperature the nature of thedrawing phenomenon changes so that the necessary incipient surface cracking is not. achieved. Temperatures below room temperature aresatisfactory. Although the use of a snubbing '50 such a manner thattensile properties are impaired. In the cracking agents to those of highmolecular weight is necessaryin order that the cracking effectbeconfined strictly to the surface of the filaments, penetration to anyextent into the interior of the fiber being prevented by the large sizeof the cracking agent molecule.

Liquid cracking agents are preferred. These agents may be pure compoundsor their solutions. S No complete list of cracking agents can be givenwhich is operable for all polymers, but the following simple testenables one to determine whether a liquid is a cracking agent or not. Inthe test a freshly spun, undrawn fiber is drawn a small amount '(about1.5 under'the surface of the liquid to be tested. By freshly spun ismeant a fiber that is less than one week old. This restriction is forthe purposes of this test only, since the process of this invention isapplicable to a wider range of aged fibers; Microscopic examination-ofthe filaments will show transverse cracks and/ or multiple neck drawingif the liquid is a suitable cracking agent. It is characteristic ofmultiple neck drawing that a lower drawing force (as much as 90% lessforce) is required in comparison with conventional (single neck) colddrawing under the same temperature and speed conditions,

drawing procedures.

pin is not required in the predrawing step, it may be used if desired,and in "some instances gives more satisfactory results.

Following the predrawing step, the filament is further thicker sectionshave a diameterat least 30% greater ditions which disassociate thefilament from the influence of the cracking agent, so that an orientedfilament having good tensile properties is produced as in normal In thissecond drawing step the influence of the cracking agent can bedisassociated by drawing at a temperature at which the cracking agent isno longer active, e.g., above 80 C., or by removing the cracking agentfrom the filament by evaporation, washing, or wipi ng the filament. Inorder to draw at least 1.5 times in thls second step, the filamentorientation must be sufliciently low prior to the predrawing step.Preferably, the initial .undrawn filament is substantially unoriented,i.e., has a birefringence that is less than 10% of the maximum possible,since this provides for more effective surface modification.

H; J. Woods, in the Journal of the Textile Institute Transactions, Vol.46, pages 629-631 published September 1955, has described a phenomenonof surface cracking in unoriented synthetic polymers and has shown thatdrawing nylon filaments in the presence of certain cracking agents suchas ethanol or acetone, leads to an oriented fiber with a certain degreeof surface roughness. Woods. procedure applied to polyethyleneterephthalate is found to produce filaments having a configurationsimilar to a turned bedpost, i.e., the filaments have asuccession ofabrupt changes in diameter in which the thicker sections have a diameterat least 30% greater than the thinner sections. The phenomenon describedby Woods differs from the invention described herein not only in thesize of the non-uniformities imparted to the individual filaments, butalso differs in the fact that the process described by Woods alwaysresults in a fiber having a reduced tensile strength, which is thoughtto be a result of the presence of numerous voids observed at thejunctions between fiber segments. In contrast, the fibers of thisinvention are substantially equivalent in tensile strength toconventionally drawn smooth-surfaced fibers.

The coefiicient of hydrodynamic friction used herein is measured byhanging a test filament over a /z-inch diameter polished chrome-platedmandrel so that the filament contacts the mandrel over an arc ofapproximately 180. A 0.3-gram weight is attached to one end of thefilament (input tension) and a strain gauge is attached to the other end(output tension). The mandrel is rotated at a speed of 1800 y.p.m. andthe area of contact flooded with a drop of No. 50 mineral oilimmediately before strain gauge readings are made. The coefficient iscalculated from the belt friction equation:

where j is the coeificient of hydrodynamic friction, T is the inputtension, T is the output tension, and on is the angle of wrap. In thistest, a commercially available terephthalate polyester yarn is found togive values in the range 0.6 to 0.7 on the particular mandrel employed.

The following examples are presented to illustrate the invention, andare not intended to be limitative.

Example I Polyethylene terephthalate is melt spun to produce an undrawn,34-filament yarn having a total denier of 210. A 15% aqueous emulsion ofbutyl stearate is applied to the undrawn yarn which is then wound on apackage and stored for 3 Weeks. The aged yarn is then drawn in twostages by passing the yam over a feed wheel having a peripheral speed of100 feet per minute, then around a -inch diameter unheated stationaryceramic snubbing pin, then around a draw roll rotating at 110 ft./min.,around a l fit-inch diameter ceramic stationary snubbing pin heated to atemperature of 90 C., then around a second draw roll rotating at asurface speed of 330 ft./min., and finally to a windup.

The yarn produced is examined under a light microscope at 200xmagnification and the filaments found to have a smooth surface with nosignificant number of bumps or nodules. No voids or bubbles areapparent. Birefringence measurements indicate uniform molecularorientation along the length of the filaments.

The yarn is examined by means of an electron microscope using standardreplica techniques and the filaments found to have a surfacecharacterized by randomly spaced, circumferential ridges occurring at anaverage frequency of about 60 ridges per millimeter along the length ofthe filament. The average height of the ridges above the surface of thefilament appears to be about 0.09 micron. The filament diameter is about14 microns. Measurement of the hydrodynamic friction coefficient of theyarn gives a value of about 0.43 (as measured on a /z-inch diameterpolished stainless steel mandrel rotating at a speed of 1800 y.p.m.).This value is in sharp contrast to a value of 0.74 exhibited by asimilar yarn drawn in the same way with the exception that the firstdraw stage (predraw) is eliminated.

The general procedure described above is repeated, using 15% aqueoussolutions or emulsions of the following cracking agents, instead ofbutylstearate, and the coefficient of hydrodynamic friction measured togive the results shown in the following table:

Cracking agent: 1'- Polyethylene oxide (400 mol. Wt.) 0.48 Polyethyleneoxide (600 mol. wt.) 0.47 Poly(ethylene glycol) monolaurate 0.46Oleylalcohol/9 mols ethylene oxide 0.50

Copolymerized ethylene glycol/propylene glycol (random) 0.49 Eicosane0.54 Isopropyl myristate 0.55

The low coefficient-of-friction values shown in the table correlate wellwith the reduced running tensions and improved processability shown bythese yarns.

Example 11 Polyethylene terephthalate is melt spun to give an undrawnyarn of 4.5 denier per filament. During spinning a polyethylene oxide ofmolecular weight 400 is applied to the filaments as a spinning finishfrom an aqueous solution. The undrawn yarn is aged for 2 days. Yarn endsfrom 25 bobbins are then combined to form a tow of 50,000 total denierand drawn as follows: The tow is passed around a set of feed rollsrotating at peripheral speed of 60 ft./min., then passed in an S-shapedwrap around a pair of /z-inch polished stainless steel stationarysnubbing pins, and then around a second set of rolls rotating at aperipheral speed of 63.5 ft./min., then passed through an aqueous bathmaintained at C., then around a third set of draw rolls rotating at aperipheral speed of 203 ft./min. The drawn tow is crimped to give anominal 8 crimps per inch, relaxed for 5 minutes at 105 C. in an oven,and then cut to give a staple in which the filament length is 1 /2-inCh.The staple is then carded and spun into a yarn on the cotton system.

A control sample is prepared from the same supply yarn in a similarfashion with the exception that the firststage snubbing pin iseliminated and the speeds of the first and second set of rolls are thesame, i.e., there is no predrawing step.

Tests carried out on the two above items to show tensile and frictionalproperties gave the results shown in the following table:

The test staple is examined under an optical microscope and found tohave the smooth surface normally associated with melt-spun fibers. Underthe electron microscope, however, the surface of the filaments is foundto possess randomly distributed, transverse ridges occurring along thelength of the filament at a frequency of about ridges per millimeter.The average height of the ridges appears to be about 0.10 micron. Mostof the ridges appear to travel more than halfway around thecircumference of the filaments, but do not appear to make a completecircle. No significant number of bumps or nodules are found on thefilaments.

Example Ill Polyethylene terephthalate containing 0.3% TiO delusterantis melt spun to give a 34-filament yarn having a total denier of 210.During spinning, an aqueous finish containing polyethylene oxide ofmolecular weight 400 is applied to the filaments. The filaments are aged30 days and then drawn in a two-stage process as follows. In the firststage the filaments are drawn to 1.05 times the 7 a original length atroomtemperature with a snubbing pin in the draw zone.

ln the'second stage the filaments are ."ments) is melt s puri and a 15%emulsion of butylstearate passed around a draw pin heated to 95 C. anddrawn to 3.0 times greater length. "(The filaments have a tenacity of3.6,g.p.d. at. a break elongation of 20%.

The filaments producedabove are examined by optical microscopy and foundto have the smooth surface characteristic of melt spun fibers. orsections of enlarged diameter. are apparent. V

The filaments are examined in profile by electron microscopy and foundtopossess surface bumps which occur with a frequency of about 50 ridgesper millimeter along the filament. The average height of thebumps abovethe surface of the filament is found to be about.0.07 micron. Whensurface replicas are prepared and examined by electron microscopy, theabove-observed bumps are found to be transverse ridges extending for themost part .more than half-way around the'filament. 5

A control yarn prepared in a similar fashion, with the exception thatno. predrawnstep is used, is found to have No bumps, protuberances,

" 2.8times its length ona third set of rolls operating at :1

erties of these three yarns are tabulated below:

a smooth surface by optical microscopy and also by elecf tronmiscroscopy. 7

Measurement of the hydrodynamic friction coefiicientof the test andcontrol yarns gives a valueof about 0.55

for ridged test yarn anda value of about 0.67 for the smooth controlyarn.

' Example IV A copolyrner of polyethylene terephthalate containing" 2mol percent S-sodiumsulfoisophthalic acid, and with no TiO present, ismelt spun to give a 34-filament yarn having a total undrawn denier of-230. Y-shaped spinneret;

holes are used and the quenching condition adjusted so that the yarnproduced has a trilobal cross-section of the type disclosed in FIG. ZofHolland US. Patent No. 2,939,201, dated June 7, 1960. Duringspinning,poly ethylene oxide of molecular weight 400 is applied to theperipheralspeed of250 ft./ min. The yarn is then relaxed for 6 minutes at 140 C.under no load. Item B is prepared similarly, except that the yarn is notsnubbed in the first drawzone Item C is prepared similarly to items Aand B except that no snub is used inthe first stage and the speed of thesecond set'of rolls is set at 90 ft./min. so that no drawing takes placein the first stage. The prop- Tenacity, Elonga: Initial 100 0. Itemg.p.d. V tion, modulus, shrinkage f 1 percent g.p.d.

Examination of the three yarns by means of an electron microscope showsthat control item C is made up of smooth-surfaced filaments in contrastto items A and B which show numerous circumferential ridges, in accordwith the present invention.

..Exa mple VI A series of textile yarns are melt spun from severaldifferent polyesters and the undrawn yarn aged in contact yarn as anaqueous finish. After aging for '3 days, the p yarnis drawn at roomtemperature'to 1.06 times its length with the draw taking place on anunheated ceramic snub bing pin. Subsequently, the yarn is drawn to 2.7times itslength over a snubbing pin immersed in bath maintained at atemperature of 90 C. 7

Measurement of the tensile properties of the yarn gives values of 2.75g.p.d. for tenacity and 25% for break elongation.

an aqueous is used.

Examination of the test yarn by optical microscopy revealed filaments ofsmooth profile having no visible bumps or significant changes in yarndiameter. However, the filaments do exhibit a number ofrandomly'dispersed transverse flines which are vunresolvable under thelight, microscope, and which occur with a frequency of about;

80 ridges per millimeter. v

Surface replicas of the test filaments are observed under an electronmicroscope; The surface is characterized by a series of randomlyspaced,'discontinu'- These values are substantially the same as, thoseobtainedfor a control yarn prepared in exactly'the' same manner with theexception-that no predrawing step.

prepared and with butylstearate'for three days. The aged, undrawn yarnsare the'predrawn at a .draw ratio of 1.1, using a 3/ 16-inch diametersnubbing pin in the draw zone. ,These predrawn yarns are then furtherdrawnover a hot pin to give a total draw of about 3.0 times. Examinationof the .drawnfilamentsby electron microscope shows the presence ofcircumferential ridges occurring at a frequency lowing table.

Copolyester of ethylene ephthalate/isophthalate) (90/10 mol ratio),poly(ethylene terephtha1ate[hexahydroterephthalate) (90/ '10 and /20),poly[ethylene terephthalate/S-(sodium sulfo)isophthalate] [965/35],poly(ethylene 2,6-naphthalene dicarboxylate), poly[ethylene 2,6-naphthalenedicarboxylate/S-(scdium sulfo)isophthalate] (97/3).

0 Example V k A polyethylene terephthalate'yarn (4.5 d.p.f., 140 fila-Thepolyester of 2,6-bisinthe range of 35 to 55 ridges per millimeter.

Control samples are prepared in a similar manner, but with thepredrawingstep eliminated. Examined by electron microscope, thefilaments are foundto have a smooth surface. 1 a

I The test andcontrol yarns are tested for coeificient of hydrodynamicfriction, with the results shown in the fol- In the table, 1 values inthe column labeled flooded are from a test carried out. as described. inExampleI. Coeificient values in the. column marked film are from a testsimilar to that in Example I, with the exception that the drop of oil iswiped off the mandrel- Film Flooded Polymer Test C ontrol Test Controlglycol, terephthalic acid and hexahydroterephthalic acid (acid mol ratio83/17) The copolyester of ethylene glycol, terephthalicacid, and sebaeicacid (acid mol, ratio /10)"; The polyester of ethylene glycol andbibenzoic acid;

0. 83 0. 78 hydroxymethyldecalin and bibenzoie acid The copolyester ofhexahydrop=xylylene glycol, bibeuzoio'acid and i50 propylidene dibenzoicacid (acid mol ratio 90/10) The data in the table clearly show theimproved frictional properties of the fibers of this invention.

Although the examples above show the application of the principles ofthe present invention in connection with certain specific polyesterfilaments, it is obvious that any fiber which cold draws, and whichpossesses a surface which can be caused to crack by extending the lengthof the filament up to about after proper aging treatments, can beemployed to give ripple-surfaced filament products of the typedescribed. Thus, many other melt-spun polyester filaments are alsouseful for providing the products of this invention.

Because of their commercial availability, ease of processing andexcellent properties, the condensation polyesters and copolyesters,particularly those that can be readily melt spun, are preferred forapplication in this method. Suitable polyesters are described, forexample, in US. Patents Nos. 2,465,319, 3,018,272, 3,057,826, 3,057,827,and 2,901,466.

In a preferred embodiment of the invention, the fiberforming polymer isa synthetic linear condensation polyester of bifiunctional ester fonmingcompounds wherein at least about 75% of the repeating structural unitsof the polymer chain include at least one divalent carbocyclic ringcontaining at least six carbon atoms present as an integral part of thepolymer chain and having a minimum of four carbon atoms between thepoints of attachment of the ring in the polymer chain (para-relationshipin the case of a single 6-membered ring) The polyesters may be derivedfrom any suitable combination of bifunctional ester-forming compounds.Such compounds include hydroxy acids such as 4-(2-hydroxyethyl)benzoicacid and 4fl(2-hydroxyethoxy)benzoic acid, or mixtures of the varioussuitable bifunctional acids or derivatives thereof and the varioussuitable dihydroxy compounds and derivatives thereof. The repeatingstructural units of the polymer chain comprise recurring divalent esterradicals separated by predominantly carbon atom chains comp-risinghydrocarbon radicals, halogen-substituted hydrocarbon radicals, andchalcogen-containing hydrocarbon radicals wherein each chalcogen atomsis bonded to carbon or a different chalcogen atom, and no carbon isbonded to more than one chalcogen atom. Thus, the repeating units maycontain ether, sulfonyl, sulfide, or carbonyl radicals. Sulfonate saltsubstituents may also be present in minor amount, up to about 5 molpercent total sulfonate salt substituents in the polyester based on thenumber of ester linkages present in the polyester. Other suitablesubstituents may also be present.

Among the various suitable dicarboxylic acids are terephthalic acid,bromoterephthalic acid, 4,4'-sulfinyldibenzoic acid 4,4-dip*henic acid,4,4-benzophenonedicarboxylic acid, 1,2-bis(4-carboxyphenyl)cthane,1,2-bis(pcarboxyphenoxy)ethane b-is-4-carboxyphenol ether and various ofthe naphthalenedicarboxylic acids, especially the l,-4-, 1,5-, and2,7-isomers. Isophthalic acid is also suitable, especially when used incombination with a 1,4- dihydroxyaromatic compound. Carbonic acid issimilarly suitable.

Among the various suitable di hydroxy compounds are the glycols, such asethylene glycol and other glycols taken from the series HO(CH OH, wheren is 2 to 10; cisor trans-p-hexahydroxylylene glycol; diethylene glycol;quinitol; neopentylene glycol; 1,4-bis(hydroxyethyl)- benzene; and1,4-bis(hydroxyethoxy)benzene. Other suitable compounds includedihydroxyaro-matic compounds such as2,2-bis(4-hydroxy-3,S-dichlorophenyl)- propane, hydroquinone, and 2,5-or 2,6-dihydroxynaphthalene.

Since many diiferent embodiments of the invention may be made withoutdeparting from the spirit and scope thereof, it is to be understood thatthe invention is not limited by the specific illustrations except to theextent defined in the following claims.

I claim:

1. A substantially oriented synthetic linear condensation polyesterfiber having a surface characterized by a series of randomly spaced,discontinuous circumferential ridges of sub-microscopic size occurringwith a frequency between 10 and 130 ridges per millimeter along thelength of the fiber, the fiber being free of diameter variations inexcess of 5% of the base fiber diameter.

2. A fiber as defined in claim 1 wherein the ridges are of such lengththat the arc is at least of the circumference.

3. A fiber as defined in claim 1 wherein most of the ridges are atangles between 70 and to the direction of the fiber axis and have aheight within the range 0.07 to 0.12 micron.

4. A fiber as defined in claim 1 which is free from voids or dispersedinsoluble particles other than conventional delusterants.

5. A fiber as defined in claim 1 wherein the fiber is composed ofethylene terephthalate linear condensation polyester.

References Cited by the Examiner Kunze: Reyon Zellwolle and andereChemiefasern, Jahrq. 32, Heft 11, November, 1954, pp. 703-708. (PP. 703and 704 of interest only) EARL M. BERGERT, Primary Examiner.

1. A SUBSTANTIALLY ORIENTED SYNTHETIC LINEAR CONDENSATION POLYESTERFIBER HAVING A SURFACE CHARACTERIZED BY A SERIES OF RANDOMLY SPACED,DISCONTINUOUS CIRCUMFERENTIAL RIDGES OF SUB-MICROSCOPIC SIZE OCCURRINGWITH A FREQUENCY BETWEEN 10 AND 130 RIDGES PER MILLIMETER ALONG THELENGTH